The present invention relates to a fluid rotating apparatus such as a vacuum pump, a compressor or the like.
A vacuum pump is inevitably necessary to produce a vacuum environment for a CVD device, a dry etching device, a sputtering device, an evaporation device, etc. in the manufacturing process of semiconductors. Meanwhile, as the manufacturing environment of semiconductors has been increasingly required to be clean and of a high-vacuum in recent years, a higher standard is set for the vacuum pump.
In order to obtain a high vacuum in a semiconductor plant, a vacuum discharge system composed of a roughing pump (positive displacement pump) and a high-vacuum pump (turbo molecular pump) is constituted. After a certain level of vacuum pressure is gained from atmospheric pressure by the roughing pump, the pump is switched to the high-vacuum pump to reach a predetermined level of vacuum pressure.
FIG. 8A shows a screw-type vacuum pump as one example of a conventional positive displacement pump (roughing pump), in which reference numeral 101 represents a housing; 102 represents a first rotary shaft; 103 represents a second rotary shaft; 104 and 105 represent cylindrical rotors supported by the respective rotary shafts 102 and 103; and 106 and 107 represent thread-type grooves in the outer peripheries of the respective rotors 104 and 105. In the conventional screw type vacuum pump, the first rotary shaft 102 and the second rotary shaft 103 are arranged parallel to each other within the housing 101, having rotors 104 and 105 thereon. The rotors 104 and 105 are provided with the thread grooves 106 and 107, respectively. When the recessed part (groove) of one rotor 106 or 107 is meshed with the projecting part (land) of the other rotor 107 or 106, a space is defined therebetween. As both rotors 104 and 105 are rotated, the volume of the space is changed to thereby draw and discharge air.
FIG. 8B shows a kind of a conventional kinetic vacuum pump (high-vacuum pump), i.e., a vacuum pump of a screw groove type having a turbine blade. In the drawing, reference numeral 201 represents a housing; 202 represents a cylindrical rotor; 203 represents a turbine blade; 204 represents a screw groove; 205a and 205b represent magnetic radial bearings which support a rotary shaft 207; and 206 represents a magnetic thrust bearing. The conventional vacuum pump with a turbine blade as shown in FIG. 8B has the rotor 202 inside the housing 201, and the turbine blade 203 and the screw groove 204 formed in the lateral upper and lower parts of the rotor 202. Each of the turbine blade 203 and the screw groove 204 impresses momentum to gas molecules, to cause suction and discharge.
The conventional vacuum pumps and the vacuum discharge system of a combination of the conventional vacuum pumps described hereinabove specifically have such drawbacks as follows.